In space astronomy, astrophysics, and atmospheric studies, it is desirable to detect and sense the position of nuclear particles and ionizing radiation. The present invention relates to a highly sensitive large area nuclear radiation detector which is based on scintillating optical fibers used as a particle sensor in combination with remotely located microchannel plate photomultiplier tubes connected with the fibers and used as the detectors. The novel particle detector design is characterized by a sensitive area which is many times that of a microchannel plate, whereby large area, two-dimensional, position sensitive particle detectors may be constructed using pre-existing microchannel plates. Accordingly, the present invention is suitable for use with satellites wherein the relatively small detector is arranged within the spacecraft and the larger sensor comprising an array of scintillator fibers is deployed a few hundred meters away for determining the trajectory of particles in space.